Telephone system



Aug; 25, 925.

H. D. Ma-CPHERSKON TELEPHONE SYSTEM Filed March 4.' 1922' '7 Sheets-Sheet 1 Aug. 25, 1925. y 1,550,80

H, D. MECPHERSON TELEPHONE S YS TEM Filed March 4. 1922 Sheets-Sheet 3 OFFJCE Y 3/.7

f, Hmmm 50 AJg- 25. 1925.

H' D. MacPHERSON TELEPHONE SYSTEM '7 Sheets-Sheet 4 Filed March 4, 1922 WQ. WLEWUN'E".

Ava 25, 1925.

' 1,550,830 H. D. MacPHERsoN TELEPHONE SYSTEM Filed Maren 4.' 1922 '7 sheets-sheet 5 OFFICE Z vLL- l TEHFMWNW Aug. 25, 1925. 1,550,830

H. D. MacPHERSON TELEPHONE SYSTEM Filed March 4. 192.2

7 Sheets-Sheet 6 omcix Aug. 25, 1925.

1,550,830 H. D. MGCPHERSON TELEPHONE SYSTEM l Fileld March 4. 192.2 7 Sheets-Sheet 7 hy 7 offici Y Wil. lttlillliilllll.

Patented Aug. 25, 1925..

UNITED STATES LEE-0,3@

PATENT orifice.

HUGH D. MAcPI-IERSON, OF SUMMIT, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application led March 4, 1922.

To all 'who-m t may concern:

Be it known that I, HUGH D. MAG- PHERSON, a citizen of the United States of America, residing at Summit, in the county of Union, State of New Jersey, have invented certain new and useful Improvements in Telephone Systems, of which the following is a full, clear, concise, and eX- act description.

This invention relates to improvements in transmission systems where it is desired to determine which one of a plurality of lines has been seized and has particular reference to a signaling system wherein signals for a plurality of toll transmission lines extending between widely separated oliices are controlled over a signaling path common to such lines.

In systems of this character wherein a large number of toll lines have been employed, it has heretofore been proposed to transmit the codes of impulses over the common signaling path by means of .start-stop distribu tors. The codes of impulses, upon being transmitted, are translated to select a particular toll line at the receiving station whereupon a signaling device individual to said line is operated. Such systems have been found to be satisfactory in the results attained where installed in offices of large capacity, but in localities where only a comparatively few lines are employed, the installation of said systems has not been deemed feasible.

Other systems have been designed wherein relay mechanism is used to transmit code impulses of current over physical and phantom lines having a signaling path connected thereto and common to said lines. i

In some systems such as above referred to, should calls be initiated simultaneously on two or more lines, or should one or more of said lines be taken for use contemporaneously with the operation of the impulse transmitting mechanism, the code of impulses being transmitted by said mechanism, will be effective to cause the operation of only one signaling device at the terminating or called oiiice, and at the completion of the transmission of said code, the transmitting mechanism will again be operated to send a series of impulses individual to one of the other lines upon which another call has been initiated. ln this manner a plurality of Serial No. 541,219.

series of impulses must be successively transmitted for each line taken for use.

An object of the present invention is to determine which one of a plurality of transmission lines has been seized at a distant point. The inventive idea embodied in this object is applicable for instance to telephone or printing telegraph systems. The object is accomplished by the method and means which comprise generating an electrical effect individual to each of a plurality of transmission lines, modifying one or more of said effects in response to the seizure of one or more of said lines and transmitting the modified effects to identify the corresponding lines.

A feature of the invention comprises transmitting over a signaling path an impulse for each of a plurality of circuits adapted to be seized and in response to the seizure of any one of a plurality of said circuits.

Another feature of the invention is the provision of impulse transmitting and receiving mechanisms, each preferably including a train of relays operable, when a call is initiated on any one of a plurality of transmission lines, to transmit and receive, respectively, a series of impulses, of which one is characterized by the busy condition of the line taken for use to effect the operation of a signaling device individual to said line. If calls are initiated simultaneously, or on certain of said lines contemporaneously with the transmission of a series of im pulses, certain impulses of the series will be so characterized as to cause the successive operation of signaling devices individual to the lines taken for use.

Another object is to render more positive the transmission of impulses over a signaling path common to a plurality of toll transmission lines by preventing the transmission of an impulse until an impulse is received indieating that the first-named impulse may be properly received at a distant point. This object is preferably accomplished by the method and means which comprise transmitting an impulse over a signaling path, receiving said impulse and, in response to the receipt of said impulse, transmitting a second impulse to control the transmission of a third impulse over said path.

rlhe above and other objects, not specifiirait lll cally mentioned, will be more clearly understood by reference to the following description when taken in connection with the accompanying drawings wherein Figs. 1 to 5 inclusive, when arranged in accordance with Fig. 8, illustrate one embodiment of the inventive idea, and Figs. 1, 4, 5, 6 and 7, arranged as shown in Fig. 9, disclose another embodiment thereof.

Briefly, the invention contemplates the provision of a plurality of transmission lines, such as L1, interconnecting` two distant oilices X and Y. Impulse transmitting and receiving mechanisms are provided at each oiiice and are operable to transmit and receive series of impulses over a common signaling path joining said ollices. These series of impulses upon being received at oflice Y are utilized to control the operation of signaling devices, such as guard lamps, each individual to one of the transmission lines. The transmitting and receiving mechanisms each comprise a train ci' relays, certain of which are arranged in groups, each group being individual to one ot the transmission lines. Upon the initiation of a call on any one of the transmission lines at oihce X, the transmitting mechanism thereat is operated to send a series of current impulses over the common signaling path to the receiving mechanism at oliice Y, whereby the groups ot relays comprising said receiving mechanism are successively operated. When the groups of relays of the transmitting and receiving mechanisms individual to the line taken for use are reached in the operation of said mechanisms, an impulse of current of different potential from those transmitted for lines which have not been taken for use is sent over the signaling path, and when this impulse is received by the receiving mechanism, the group of relays of the latter mechanism which is individual to said line, is in such condition that said impulse of current will be effective to operate apparatus at the receiving oflice Y, which results in the lighting of the guard lamp individual to said line.

Should simultaneous calls be initiated on two or more of the lines, the groups of relays otl the transmitting and receiving mechanism individual to the linesI taken for use will operate together with the other groups, and as each group of relays of said mechanisms associated with the busy lines is energized, an impulse of current similar to the one above referred to is transmitted over the signaling path. Through the intermediary of the receiving mechanism, said impulses cause the successive operation of the signaling devices or guard lamps individual tp the various busy lines.

It, after a call has been initiated on one line and the impulse transmitting and receiving mechanisms have started their operations of transmitting and receiving a series of impulses, other lines which are subsequent to the first named line in the order of their appearance should be taken for use contemporaneously with the operation of said mechanisms, the character of the impulses of said series will be so changed by the seizure of said lines that said series will be eiective to cause the operation ott signaling devices individual to all of the lines upon which calls have been initiated.

It is believed that the invention will now be clearely understood from the following detailed description. The operation of the system arranged in accordance with Fig. S will first be described.

Operator at 077%@ X initiates a @all to substation S at 07720@ Z.

The operator at ofiice X, desiring to establish connection with the telephone line S at oflice Z communicates with the operator at oliice Y over an order wire circuit (not shown) to receive an assignment of an idle toll or trunk line The operator at oice X, upon ascertaining from the operator at ollice Y that the connection to substation S is to be established over toll line L1 inserts plug 100 of cord circuit A into the jack 101 ot line L1. The cord circuit A, only a portion oi' which is shown, is of a well-known design, and it will be understood that previous to the insertion of the plug 100 into jack 101, the operator at oi'- fice X has connected the answering plug ot said cord circuit with the calling subscribers line. Upon engagement of the sleeve con- `tacts of said plug 100 and jack 101, a eircuit is established which is traceable from grounded battery, through the winding of the marginal relay 102, sleeve contacts of plug 100 and jack 101, and the winding of relay 103, to ground. The relay 102, being` marginal, does not operate at this time. lielay 103, in operating, establishes a circuit extending from ground at the normal contacts of either ot the relays 104 or 105 through t-he alternate contact oit relay 103` the normal contact of relay 106, winding of slow release relay 107, common conductor 108, and the winding oit relay 200 of the transmitting mechanism at office X to grounded battery. Relays 107 and 200 operate in this circuit, the energization of the latter relay initiating the operation oi' the impulse transmitting mechanism shown in Fig. 2. The operation of relay 107 connects the positive terminal of a battery to the right-hand alternate contact of said relay for a purpose which will appear in the course of the description. The operation o't' relay 103 also closes an energizing circuit for relay 109 extending from grounded battery, through the winding and normal con- Wil. ltttlltlllhlt.

tact of said relay, and alternate contact of relay 103 to ground at the normal contacts of either of the relays 104 or 105. Relay 109 operates and locks to ground through its left-hand alternate contact, but performs no useful function at this time.

It is here noted that all slow operating and releasing relays shown in the drawings have been indicated conventionally by arrows intersecting the armatures of these relays and pointing in the direction that the armatures move slowly.

Relay 200, in operating, closes a circuit extending from ground, through the contact of relay 200, the contact of slow release relay 201, and the winding of relay 202 to grounded battery for operating relay 202. An obvious energizing circuit is also estatlished for relay 208 by the operation of relay 200, and relay 208 thereupon locks to ground at the normal contact of relay 204. lllhen relay 202 operates, ground is connected to the upper left-hand contact thereof to estab lish an obvious operating circuit for slow release relay 205. The closure of the con tact of the latter relay causes the operation of slow release relay 201, which in opening its contact disconnects ground from the winding of relay 202, which then releases to cause the release of relay 205, followed by the release of relay 201. llVhen the contact of relay 201 again closes, relay 202 is again operated to once more initiate the cycle of operation of relays 205 and 201. Each time that relay 202 is operated and released, an impulse of current is transmitted over the common signaling path P to the receiving` mechanism at office Y to accomplish the operation of relays of a train forming a part of this receiving mechanism. The operation of relay 202 also causes the synchronous operation of relays of the train included in the transmitting mechanism at oiiice X. The first energization of relay 202 establishes a circuit extending from ground, through the lower left-hand contact of relay 202, and from thence in parallel over one path, through the left-hand normal contact of relay 208, the normal contact of relay 210, and the right-hand winding of relay 209 to grounded battery, and over another path through the right-hand contact of relay 208 and the left-hand winding of this relay to grounded battery. rlhe right-hand armature and contact of relay 208 initially sliertcircuits the right-hand winding of relay 208, but said relay operates through its left-hand winding, and is held operated through both of its windings in series by the ground at the lower left-hand contact of relay 202, while the latter relay remains operated. This arrangement of the circuit of relay 208 provides for the quick operation and release thereof to insure the proper operation of the train of relays comprising the transmitting mechanism at oilice X. When relay 208 operates, ground is disconnected from the left-hand normal'contact of said relay, but before this occurs, relay 209 energizes in the circuit traced therefor, and locks through its left-hand winding and contact to ground at the left-hand contact of relay 206. The closure of the left-hand contact of relay 209 also establishes an energizing and holding circuit for relay 210, which in operating transfers the conductor connected to the lefthand normal contact of relay 208 to the alternate contact of relay 210 to prepare an energizing circuit for relay 211. The closure of the right-hand alternate contact of relay 209 connects a potential thereto which depends upon the condition of a relay associated with the first toll line (not shown), lsimilar to relay 107 individual to the line L1. Assuming that the iirst toll line is idle, it will be obvious that the relay associated therewith, which is similar to relay 107, is in its normal condition, and therefore ground will be connected to the right-hand alternate Contact of relay 209. This ground is extended through the normal contacts of the remaining relays of the train similar to relay 209, and thence to the right-hand normal contact of relay 206. lWhile relay 202 is energized, this ground has no effect. rlhe closure of the right-hand alternate contact of relay 202, during the energization thereof, connects negative battery over one path, through the lower winding of the polarized relay 207, and the artilicial line to ground, and over another path through the upper winding of said polarized relay, and over the common signaling conductor P, the windings of the polarized relay 800 at oflice Y, and the artificial line to ground. The current in 'this path has no effect on the relay 207, but causes the relay 300 to close its upper contact, thereby establishing a circuit extending from ground, the upper contact of relay 800, from thence over one path through the left-hand contact and righthand winding of relay 801, similar to relay 208, to grounded battery, and over another path through the right-hand normal contact of relay 301, the normal contact of relay 304, and the left-hand winding of relay 303 to grounded battery. Relays 301 and 303 operate, the latter relay immediately locking through its right-hand winding and contact to ground at the contact of relay 302. Relay l, in operating, provides a holding circuit for itself extending through both of its windings, and disconnects ground from its right-hand normal Contact, which is extended to the leftdiand winding of relay 803. The operation of relay 308 is followed by the energization of relay 80at through the Contact of relay 808. TWhen relay 202 re leases following the opening of its circuit by the energization of relay 201, relay 208 llt) releases, and the ground which is connected to the right-hand normal contact of relay 20G is now extended to the normal contact of relay 202, and from thence to the windings of the polar relays 207 and 300. This ground causes relay 300 to release, and thus more its armature to its neutral position, thereby disconnecting` ground from the upper contact of relay 300 to cause the release of relay 301.

Upon the next energization of relay 202, due to the release of relay 201, ground connected to the lower left-hand contact of relay 202 is extended to the left-hand normal contact of relay 208, the alternate contact of relay 210, normal Contact of relay 212, and the right-hand winding of relay 211 to grounded battery, causing the operation of the latter relay, which then locks through its left-hand winding and contact to ground at the left-hand contact of relay 206. The ground connected to the lower left-hand Contact of relay 202 also causes the operation of relay 208, as previously described, to disconnect the ground from the left-hand normal contact of relay 208. The closure of the upper left-hand contact of relay 202 again initiates the cycle of operation of relays 205 and 201 to cause the release of relay 202. The operation of relay 211 in the circuit described therefor causes the energization of relay 212 over an obvious circuit, and the closure of the right-hand alternate contact of relay 211 connects a potential to the right-hand normal contact of relay 206, which depends upon the condition of a relay associated with the first toll line, similar to the relay 110 individual of the toll line L1. This relay similar to 110, being in its normal position, a ground potential is connected to the right-hand normal Contact of relay 206. The operation of relay 212 connects ground in series through the right-hand normal contacts of relays 222, 220, 218, 216 and 21A, the right-hand alternate contact of relay 212, to the left-hand contact of a relay associated with the rst toll line, similar to relay 107. Since it is assumed that this relay associated with the first toll line is in its normal condition, the ground has no effect.

The second operation of relay 202, again connects negative battery through the righthand alternate contact of said relay to the windings of the polar relays 207 and 300, thereby causing the latter relay to close its upper contact in the same manner as previously described. The ground connected to said upper contact is now extended through he right-hand normal contact of relay 301, the left-hand alternate Contact of relay 304, the left-hand normal contact of relay 30G, and the left-hand winding of relay 305 to grounded battery, causing the operation of the lat-ter relay, which then locks through its right-hand Winding and Contact to ground at the contact of relay 302. The ground connected to the upper contact of relay 300 also energizes relay 301 to disconnect said ground from the winding of relay 305. Then relay 305 closes its contact, relay 306 operates over an obvious circuit, and is held operated by the ground at the contact of re lay 302, lVhen the relay 202 releases in the second cycle of operation of relays 201, 202 and 205, the ground which is connected to the right-hand normal contact of relay 206, through the right-hand alternate contact of relay 211, and the normal contact of the relay associated With the first toll line similar to relay 110, is extended through the normal contact of relay 202, to the windings of the polar relays 207 and 300, causing the release of the latter relay, which is followed by the deenergization of relay 301.

When relay 202 next operates to transmit the third impulse of current over the common signaling path P, the round at the lower left-hand contact of reday 202 is eX- tenced through the left-hand normal contact of relay 208, through the left-hand alternate contacts of relays 210 and 212, the left-hand normal contact of relay 214, and the righthand winding of relay 213 to grounded battery. Relay 213 operates in this circuit and locks in an obvious manner, and relay 208 energizes, as before described. The closure of the left-hand contact of relay 213 causes the energization of relay 214;, while the closure of the right-hand alternate contact of relay 213 connects positive battery from the right-hand alternate contact of relay 107, which is now operated, to the righthand normal contact of relay 206, through the normal contacts of relays 215, 217, 219 in series. rlhis battery potential has no effect until relay 202 releases. While the latter relay is operated, negative battery is connected to the windings of the polar relays 207 and 300, through the right-hand alternate contact of relay 202, causing the relay 300 to close its upper contact. The ground now connected to this contact is eX- tended through the right-hand normal contact of relay 301, the left-hand alternate con tacts of relays 304 and 306, the left-hand normal contact of relay 308, and the lefthand winding of relay 307 to grounded battery. Relay 307 energizes in this circuit and locks in an obvious manner, and after the energization thereof, relay 301 operates as before described. The closure of the contact of relay 307 closes an obvious circuit for operating relay 308.

lVhen relay 202 releases for the third time during the operation of the impulse control relays, relay 208 deenergizes, and upon closure of the right-hand normal contact of relay 202, the positive battery connected to the right-hand alternate contact of relay 107 is then extended through the right-hand normal contact of relay 206, the normal Contact of relay 202, and the windings of polar relays 207 and 300 to ground through the artificial line. This positive impulse of current transmitted over the signaling path P causes the relay 300 to close its lower contact, thereby causing the release of relay 301. The ground now connected to the lower contact of relay 300 is extended to the righthand normal contacts of relays 3141, 312 and 310, right-hand alternate contact of relay 308, and from thence in parallel through the middle winding of the differential relay 400, and the lefthand winding of relay 4101 to the grounded battery. Relays 400 and 401 operate in this circuit, and the former locks through its rightdiand wind ing. The effect of the operation of these two relays will presently be described.

The fourth energization of relay 202 in the cycle of operation of the impulse cont-rol relays now connects ground from the lower left-hand contact of relay 202, through the left-hand normal contact of relay 203, the alternate Contact of relay 210, the left-hand alternate contacts of relays 212 and 214, the left-hand normal Contact of relay 216, and the' right-hand winding of relay 215 to grounded battery. Relay 215 energizes and locks, and by the closure of its lefthand contact causes the energization of relay 216. When the latter relay closes its right-hand alternate contact, a circuit is established for relay 106 extending from grounded battery, through the winding of said relay, the left-hand contact of relay 107, right-hand alternate contact of relay 216, and the right-hand normal contact of relays 218, 220, and 222 in series, to ground. Relay 106 energizes and loclrs through its winding and left-hand Contact, the alternate contact of relay 103, and left-hand normal contact of relay 105, to ground. In opening its alternate contact, relay 106 breaks the holding circuit for relays 107 and 200, and these relays thereupon release. The release of relay 107 disconnects positive battery from the right hand normal contact of relay 206. The release of relay 200 removes the control of the operation of the relay 202 from the relay 200 and transfers it to relay 204, which has ground connected to its normal contact. This ground controls the succeeding operations of relay 202, as will presently appear. The operation of relay 202 again connects negative battery to the rightehand alternate contact thereof to cause the polar relay 300 to close its upper Contact, whereupon the ground connected to this contact is extended through the right-hand normal contact of relay 301, the left-hand alternate con-A tacts of relays 304, 306 and 308 in series,

the left-hand normal contact of relay 310 and the left-hand winding of relay 309 to grounded battery. Relay 309 operates and locks, and in closing its contact establishes an obvious energizing circuit for relay 310. Relay 301 again operates following the closure of the circuit for relay 300 and disconnects the ground at the upper Contact of relay 300 from the right-hand normal Contact of relay 301. When relay 202 releases for the fourth time, relay 208 deenergizes, and upon closure of the normal contact of relay 202, ground is connected through the normal contact of relay 110, the right-hand alternate contact of relay 215, the normal contacts of relays 217 and 219, right-hand normal contact of relay 206, normal contact of relay 202, and from thence to the windings of polar relays 207 and 300, causing the latter relay to restore its armature to its neutral position and thereby disconnect ground from the upper contact thereof, causing the release of relay 301.

Relay 202 now operates for the fifth time, and the circuit therefor in this and succeeding operations extends from grounded battery, through the winding of relay 202, contact of relay 201, contact of relay 203, which is energized and locked, and the normal contact of relay 204 to ground, relay 200 being now released, as previously described. Vhen relay 202 closes its lower left-hand contact, relay 217`operates and locks in a manner, which is now believed to be obvious from an understanding of the description of the operation of other similar relays, and upon energization of relay 217, relay 218 operates. Relay 203 energizes in the same manner as before described. The o-peration of relay 202 again connects negative battery to the rightehand `alternate contact of said relay to transmit an impulse of current of negative polarity over the path P to cause polar relay 300 to close its upper contact. In a manner which is now believed to be obvious, connection of ground to the upper contact of relay 300 causes the operation and locking of relay 311 and the energization of relays 312 and 301. Then relay 202 releases for the fifth time, the ground which is found at the normal contact of the relay associated with the last toll line similar to the relay 107 of line L1, is extended through the right-hand alternate contact of relay 217 the normal contact of relay 219, the right-hand normal contact of relay 206, the normal contact of relay 202, and from thence to the windings of the relays 207 and 300, causing the latter relay to open its upper contact, following which relay 301 releases.

The sixth energization of relay 202 is followed by the energization and locking of relay 219 and the operation of relays 208 and 220 in a manner which is now believed to be obvious. The operation of relay 202 causes relay 300 to again close its upper contact, whereby relays 313, 314 and 301 are operated. The sixth release of relay 202 causes the deenergization of relay 208 and the connection of ground from the normal contact of the relay associated with the last toll line similar to relay 110, to the right-hand alternate contact of relay 219, from whence said ground is extended through the righthand normal Contact of relay 20G and normal contact of relay 202 to the windings of relays 20'! and 300, causing the latter relay to open its upper contact, following which relay 301 again releases.

The seventh and last operation of relay 202 effects the operation of relays 221, 222 and 20S, and when relay 222 energizes, an obvious operating circuit for relay 204 is established. The latter relay energizes to open the locking circuit of relay 203, which then releases to permanently open the energizing circuit of relay 202 so that this relay will not again operate after its seventh release. The closure of the alternate con tact of relay 204 causes the energization of relay 206, which, in disconnecting` ground from its left-hand contact, opens the lool@ ing and holding circuits of relays 209 to Q22, inclusive, whereupon these relays restore to normal. The deenergization of relay 222 opens the circuit for relay 204, which then releases, followed by the release of relay 206. However, before this action takes place, relay 300 is caused to again close its upper contact by the energization of relay 202 so as to bring about the operation of relays 315, 301 and 302 over circuits which are now believed to be obvious. lVhen relay 302 operates, the ground is disconnected from the contact thereof to open the holding and locking circuits for relays 803 to 315, inclusive, and these relays thereupon restore to normal. lhen relay 302 operates, it interrupts its own energizing circuit, and hence said relay will immediately deenergize. lVhen relay 202 releases for the seventh time, ground is connected to the normal Contact thereof from the alternate contact of relay 206, which has not yet released, and this ground causes relay 300 to open its upper contact, thereby restoring relay 301. The cycle of operation of the trains of transmitting and receiving relays has now been completed, and a series of impulses individual to the line L1 has been transmitted over the common signaling path P and received at otiice Y in such a manner as to select mechanism thereat individual to the line L1.

Returning to a point in the operation where relays 400 and 401 were operated by the connection of ground to the lower contact of relay 300, and relay 400 was locked,

it will be obvious that relay 401 is not locked after its energization due to the fact that relay 402 is not operated. Therefore, as soon as the impulse of current has been terminated and the lower contact of relay 300 is opened, as described, relay 401 restores, thereby establishing a circuit for the slow release relay 403 from grounded battery through the winding of relay 403, the normal contact of relay 401 and the right-hand alternate contact of relay 400 to ground. Relay 403 energizes and establishes an obvious operating circuit for the slow release relay 402. The operation of relays 402 and 403 have no effect at this time. Vhen relay 400 operates, guard lamp 404 individual to line L1 is lighted over a circuit extending from grounded battery, through the lamp 404, the right-hand normal contact of relay 405 and the right-hand alternate contact of relay 400 to ground. The lighting of the lamp 404 serves as a signal to the operator at office Y, indicating that the operator at oitice X has connected the cord circuit A to the proper toll line L1.

Connection of toll switching trim-7c circuit il! with the telephone Zine S.

At the time that the operator at office Y designated the toll line L1 with which the operator at oi'lice X should connect the cord circuit- A, vthe operator at office Y also communicated with the operator at office Z over an order wire circuit (not shown), informing the operator at office Z as to the number of the desired line, whereupon the operator at oiiice Z designates the toll switching trunl circuit over which the connection should be established. Assuming the toll switching trunk M to be that designated, the operator at oiiice Z, after designating this trunk, inserts the plug 500 into the jack 501 of the telephone line S. Relays 502 and 503 then operate over an obvious circuit, through the sleeve contacts of plug 500 and jack 501. The operation of relay 503 disconnects the line relay 504 from the telephone line, and thus prevents the operation of said relay and consequent lighting of line lamp 505 when the subscriber at the called substation removes his receiver from its switch hook in answer to the ringing of his call bell. The operation of relay 502 establishes a circuit for the supervisory lamp 506 extending from grounded battery, through the lamp 506, the right-hand alternate contact of relay 502, resistance 507, and the normal contact of re lay 508 to ground.

Operator at ao@ Y oon/accts toll Zinc L1 to the 'oZZ switching tru/alf; M.

switching trunk M, and thereby causes the afa,

l tireless.

Cil

successive euergizations of/ relays 406 and 405 over obvious circuits. The energization of the latter relay opens its right-hand normal contact, and thereby extinguishes the lamp 404. The operation otl relay 405 also establishes a circuit for the supervisory relay 410 and the relay 508 in the trunk circuit M, said circuit being traceable from grounded battery, through the lett-hand winding of relay 508, outer normal contact of relay 509, the tip contacts of jack 408 and plug 407, the lett-hand alternate contact of relay 405, the upper normal contact of relay 409, Winding of the supervisory relay 410, the outer left-hand alternate contact ot relay 400, the lower normal contact of relay 409, ring contacts of plug 407 and jack 408, the inner normal contact of relay 509, and the right-hand winding of relay 508 to ground. The energization of relay 508.` opens the circuit of and extinguishes the lamp 505.

The energization of the supervisory relay 410 establishes a circuit extending from ground, through the alternate contact. ot this relay, and from thence in parallel over one path through the winding of slow release relay 411, over another path through the left-hand contact of relay 411, the normal contact and winding of slow release relay 412, and over a third path through the winding of slow release relay 419 to grounded battery. Relays 411, 412 and 419 energize, and relay 412 is then locked through its winding and right-hand alternate contact 7 to ground. The operation of relay 419 has no eitlect at this time. The closure of the lett-hand contact of relay 412 establishes an obvious energizing circuit for relay 413, which then locks through its winding and lett-hand alternate contact to ground. The ground connected to the lett-hand contact ot relay 412 is also extended through the winding of slow release relay 414, and from thence over the common conductor 417 to battery through the winding ot a relay in the transmitting mechanism TM, similar to the relay 200. This relay and relay 414 energize in this circuit, and the energization of the former initiates the operation of the transmitting mechanism TM, which is similar in all respects to the mechanism shown in Fig. 2. The relays of the mechanism TM are now operated totransmit a series of impulses over the signaling path P to the receiving mechanism RM at oiiice X in the same manner as described in connection with the transmission ot impulses Jfrom oiiice X to otiice Y. The receiving mechanism RM at otlice X is identical with that of otlice Y, illustrated in Fig. 3, the relays of the mechanism RM being controlled by the polarized relay 207. Then the relay in the transmitting mechanism TM at office Y, similar to the relay 216, operates, ground from the normal contact of a relay similar to relay 222 is connected to conductor 316, and extended through the alternate contact of relay 414 to short circuit relay 412 and this relay thereupon releases to remove ground 'from the windings of relay 414 and the relay ot' the mechanism T114, similar to the relay 200, whereupon these relays deenergize. Before this occurs, however, the positive battery connected to the lett-hand alternate contact oit relay 414 causes the relay 207 to close its lower contact and thereby connect ground to the conductor 223, through the right-hand alternate contact of a relay of the receiving mechanism RM, similar to relay 308. FOL lowing this, the remaining relays of the transmitting and receiving mechanisms TM and RM are operated and released in the same manner as described in connection with Figs. 2 and 3. The ground connected to the conductor 223 causes the operation ot the ditterential relay 112 and relay 115, the former relay locking to ground through its letthand winding and contact, the alternate contact of relay 10S, and the left-hand normal contact of relay 105. The relay 115, however, does not loclt inasmuch as relay 114 is deenergized at this time, and relay 115 therefore restores atthe termination of the impulse which caused relay 207 to close its lower contact. right-hand contact of relay 115, a circuit is established for slow release relay 113, extending `from grounded battery, through the winding of said relay, right-hand contact of relay 115, lett-hand contact oit' relay 112, and from thence to ground over the locking` circuit ot the latter relay. The operation of the relay 113 causes the energization of slow release relay 114 over an obvious circuit. lVhen the contact of relay 114 is closed, a circuit is established extending from ground, through said Contact, the left-hand normal contact of relay 115, the right-hand contact of relay 105, resistance 111, sleeve contacts of jack 101 and plug 100, and the winding of marginal relay 102 to grounded battery. The inclusion of the resistance 111 in this circuit, in parallel with the winding ot' relay 103, permits relay 102 to energize, and in so doing` an obvious circuit is established for lighting the lamp 117. The lighting of this supervisory lamp serves as a signal to the operator at oiiice X that the connection has been completed through to the wanted line, and that the circuit is now in condition for operating the call bell at the substantion S.

Operator at Ofic@ X actuazfes the ringing lacy.

The operator at oitice X upon observing the lighted condition of the lamp 117, new actuates ringing key 118, and thereby eonnects a source of ringing current to the tip and ring contacts ot the jack 101 and plug Upon the closure of the i 100, which operates the ringing response relay 104 bridged across the line L1. Relay 104, in closing its alternate contact, estalilishes an obvious energizing circuit for slow release relay 105. rl`he opening of the lefthand normal contact of relay 105 breaks the locking circuit for relay 10o, which thereupon releases. rlhe locking circuit for relay 112 is also temporarily opened by the energization of relays 104 and 105, but relay 112 does not release before the alternate contact of relay 105 is closed, and therefore relay 112 will remain in its locked condition. The opening of the right-hand contact of relay 105 causes the release of marginal relay 102 and the extinguishing; of the supervisory lamp 11T. lVhen the opeator releases the ringing` lzey, relays 104 and 105 release, whereupon the marginal relay 102 is again operated to light the lamp 117.

When relay 106 releases at the time relay 105 is energized, a circuit is established eX- tendinp; from ground, through the alternate contacts of relays 105 and 103, and from thence over the previously described energizingcircuit of relays 107 and 200. Relays 10iand 200 again energize to initiate the operation of the transmittingi mechanism at ollice X to transmit yer the common signaling path a series of current impulses identical with the series which was orieinally sent at the time the call was initiated. The circuit for relays 107 and 200 is maintained after the operator restores the ringing` key 118 to normal, since ground is connected to the normal contact of relay 104 and hence to the windings of relays 107 and 200 before the relay 105 opens its alternate Contact. During the operation of the transmitting mechanism at ollice X, relay 10G is again operated and locked., and relays 107 and 200 decnerpgized, as previously described. The series of impulses now transmitted is received by the mechanism at oliice Y, and when relay 808 of. this mechanism is operated and .relay 300 closes its lower contact, `ground is connected to the middle winding of relay 400 and the lcft-hand winding of relay 401. Relay 400 is unaffected since said relay is already locked, but relay 401 is energized by this ground, and since relays 402y and 403 are now operated. relay 401 locks through its right-hand windine; and contact to `around at the contact of relay 402. Upon the closure of thel alternate contact of relay 401. a circuit is established extending' from around, through the contact of relay 402, the alternate contact of relay 401, and from thence in. parallel through the windings of slow release relays 415 and 409 to grounded battery. These relays operate, and the former in connecting lground to its Contact, establishes a temporary holding` circuit for relay 411 and energizes relay 419. Relay 409, in operating, connects a source of ringing current to the tip and ring contacts of plug` 407 and jack 408 to operate the ringing response relay 510 of the toll switching trunk M. lllhen relay 409 opens its normal contacts, the circuit for the supervisory relay 410 is opened and this relay thereupon releases, but inasmuch as relays 411 and 419 are maintained energized by the energination of relay 415, the ground connectcd to the front contact of relay 410, upon release of this relay. has no effect at this time. rl`he cnergization of relay 409 also opens the circuit for relay 508, but before this relay can release, a temporary holding` circuit is provided therefor, extending from grounded battery, through the lefthand winding of relay 508, the outer normal contact of relay 509, tip contacts of jack 408 and plug 407, the left-hand alternate contact of relay 405, and the upper alternate contact of relay 409 to ground. lllhen relay 401 operates, the holding,` circuit for slow release relay 403 is opened, and this relay, after an interval, releases to open the holding' circuit for slow release relay 402, which in releasing disconnects ground from the locking' windingl of relay 401 and the windings of relays 415 and 409. Due to the slow release nature of relays 402, 403 and 409, a sufficient time interval is provided for proper application of ringing current to the called line. The release of relay 402 is followed by the release of relay 401, whereupon relays 403 and 402 again operate. During` the time that relays 409 and 415 are operated, relay 510 remains energized, and the closure of the contact of this relay establishes a circuit extending from ground, through said contact, winding of the ringinnY relay 511, and the left-hand winding of relay 509 to grounded battery. Relays 509 and 511 energize in series, and the operation of the former provides a holding circuit for relay 508 extending' from grounded battery, through the left-hand windingr of relay 508. to `ground at the alternate contact ot relay 509, thereby maintainingr the relay 508 in its operated. condition and preventing` the lighting;- of the lamp G. The operation of relay 511 connects ringingr current to the telephone line S to operate the subscribers signal or call bell. lVhen ringine' relay 409 releases, ringing current is disconnected from the toll switching: trunk lw and ringing;n response relay 510 releases, causing" the deenereization of relay 509 and the ringing; relay 511. The release of relay 509 connects both windings of relay 508 in circuit with the supervisory relay 410 before the holding circuit established by the operation of relay 509 is opened at the alternate contact of the latter relay. Thus the relay 508 remains in its enerpized condition. The deenern'ization of relay 511 disconnects ringing` current from the line S. The series cirt t tftl1111111'n I cuit for relays 508 and 410, being again established, the latter relay operates to again close its alternate contact before the slow release relays 411 and 419 can close their contacts following the opening of the temporary holding circuit for said relays by the release of relay 415, and therefore relays 411 and 419 will remain operated over the circuit to ground at the alternate contact of relay 410. This operation of ringing the signal at substation S may be repeated until the subscriber thereat removes his receiver from the switch hook.

The .subscriber at substation S removes his receiver from zits switch hook.

In response to the operation of the signal at substation S, the subscriber thereat removes his receiver from its switch hook, thereby causing the operation of the supervisory relay 512 over a circuit extending from grounded battery, through the winding of said relay, the upper normal contact of relay 511, the tip contacts of plug 500 and jack 501, the apparatus at substation S, the ring contacts of jack 501 and plug 500, the left-hand alternate contact of relay 502, and the lower normal contact of relay 511 to ground. Relay 512 operates and causes the energization of relay 509 over a circuit extending from grounded battery, through the left-hand winding of relay 509, the contact of relay 512, the right-hand winding of relay 509, and the alternate contact of relay 508 to ground. Relay 509, in operating, closes its alternate contact and opens its normal contacts, whereby relay 508 is disconnected from the circuit including the supervisory relay 410, relay 508 being again held operated by closure of the alternate contact of relay 509. The operation of relay 509 causes the release of the supervisory relay 410, whereupon the holding circuit for slow release relays 411 and 419 is opened and said relays, after an interval, release. It will be recalled that relay 413 was operated and locked at the time that line L1 was con nected to the trunk M and a series of impulses sent to oliice X to light lamp 117 as a ringing` signal, and therefore at this stage of the operation, with relays 410, 411 and 419 released, a circuit is established extending from ground, through the normal contact of relay 410, the right-hand contact of relay 411, the Contact of relay 419, the righthand contact of relay 413, winding of relay 416, and trom thence over the common conductor 417 to grounded battery through the windingof the relay in the transmitting mechanism TM, similar to relay 200. This relay and relay 416 are operated, and the transmission of a series of impulses by the mechanism TM over the common signaling path P to the mechanism RM is thereby fllitetedY Wiese the relay in the transmitting mechanism TM, similar tothe relay 215, is energized, and the impulse control relay of said mechanism, similar to relay 202, is released, positive battery is connected through the leftshand alternate contact of relay 416 to the conductor 418, and from thence through contacts of said relays in the transmitting mechanism TM, similar to relays 215 and 202, and through the polar relays 300 and 207 to ground. The impulse thus transmitted causes the polar relay 207 to close its lower contact, whereby ground is connected to the conductor 224 through contacts of relays in the receiving mechanism RM, similar to relays 314, 312 and 310, the latter being now energized at this stage of the operation. This ground connected to the conductor 224 is extended through the right-hand contact and right-hand winding of relay 112 to grounded battery. The middle and right-hand windingsl of relay 112 being differentially wound, the closure of the circuit through the right-hand winding causes relay 112 to release. The opening of 'the left-hand contact of relay 112 is followed by the release of relays 113 and 114. The removal of ground from the contact of the latter relay opens the energizing circuit, through the resistance 111, of the marginal relay 102, whereupon relay 102 restores to extinguish the lamp 117, thus indicating to the operator at office X that the subscriber at substation line S has answered the call.

During the transmission of the series of impulses, which results in the extinguishing of lamp 117, lround is connected to conductor 317 by the operation of a relay in the mechanism TM, similar to the relay 218, the right-hand alternate contact of which is connected to the left-hand contact of relay 110, which corresponds to the relay 416 at otiice Y. This ground, which is connected to conductor 317, short circuits the relay 413 and thereby causes the release thereof. The release of relay 413 opens the circuit for relav 416 and the relay in the transmitting mechanism TM, similar to relay 200, and these relays thereupon restore.

Subscriber at substation S replaces his 're @einer upon the .sw/teh hook.

lays 41,1; 412, 413. @ad el??? the relays 41a and 413 then being locked. When relay 412 closes its left-hand contact, the previously described circuit for relay 414 and the relay of the transmitting mechanism TM, similar to relay 200, is again closed to initiate the operation of the transmitting mechanism TM, whereby a series of impulses will be transmitted over the common signaling path to control the operation of the receiving mechanism RM at oilice X. This series ot impulses is similar to the one transmitted at oilice X when the line L1 was connected to the toll switching trunk M, and results in the grounding of the conductor 223 when the relay of the mechanism RM, similar to relay 308, is operated. Relays 112 and 115 being now released, respond to the grounding ot the conductor 223, and relay 112 locks as before, but relay 115 releases at the termination Ot the impulse since relay 114 is not at this time energized. The energization of relay 112 causes the successive operation of relays 113 and 114 as soon as relay 115 closes its right-hand contact, and when relay 114 now operates, the resistance 111 is again 1ncluded in lthe circuit ot the marginal relay 102, causing this relay to operate and light the lamp 117, thus indicating to the operator at office X that the subscriber at substation S has replaced his receiver upon its switch hook. During the transmission ot this series of impulses, relays 412 and 414 are released, as previously described, and at the termination of the transmission of the series of impulses, the transmitting and receiving mechanisms TM and RM are restored to normal in a manner which is now believed to be well understood.

Operator at occ X disconnects cord circuit A from Ln@ L1.

The operator at oiiice X, upon observing the lighted condition of lamp 117, now removes the plug 100 from the jack 101, causing the release ot' relays 102 and 103, and the extinguishment of the lamp 117. The release ot relay 103 opens the locking circuit of relay 106, which is energized at this time, and this relay thereupon releases. The release of relay 103 opens the locking circuit ot relay 112 and the holding circuit for relay 113. These relays thereupon release, and the release of the latter relay causes the deenergization oi relay 114. Relay 109 is energized and locked at this time, and therefore the release of relay 103 establishes a circuit extending from ground at the left-hand normal contact of relay 105, through the normal contact ot relay 103, the right-hand contact of relay 109, the winding of slow release relay 110, common conductor 108, and the winding of relay 200 to grounded battery. Relays 200 and 110 operate, and the energization ot the former again initiates the operation of the transmitting mechanism at oilice X to transmit a series of impulses over the common signaling path l? to the receiving mechanism at oiiice Y. It will be noted that during the transmission of this series ot impulses, positive battery is not connected to the right-hand alternate contact of relay 13 as in the case of the tirst series of impulses transmitted, since relay 107 is now released. However, positive battery is connected, due to the energization of rely 110, to the right-hand alternate contact ot relay 215 so that after relay 215 has been energized during the operation of the transmitting mechanism, and when relay 202 nextreleases following the energization of relay 215, the positive battery connected to the right-hand alternate contact of relay 110 is extended over the common signaling path P to cause the relay 300 to close its lowe contact. At this time, relay 310 ot the receiving mechanism has been operated, and the ground connected to the lower contact of relay 300 is therefore extended to the right-hand normal contacts of relays 314 and 312, the right-hand alternate contact ot relay 310, and the inner lett-hand contact and lett-hand winding ot' differential relay 400 to grounded battery. The lett and middle windings of relay 400 being diiferentially wound, the closure of the circuit through the lett-hand winding thereof causes this relay to release. The eltect of the release ot this relay Will presently be described.

Then relay 218 of the transmitting mechanism at otlice X operates, ground at the normal Contact of relay 222 is extended through the right-hand normal Contact ot relay 220, the right-hand alternate contact of relay 218, the lett-hand contact ot' relay 110 to the winding of relay 109, thereby short circuiting relay 109 and causing the same to release. The opening of the righthand contact of relay 109 breaks the circuit for relays 200 and 110, and these relays thereupon restore. The operation ot the remaining relays in the transmitting mechanism at otlice X is then under the control ot relay 204, as previously described. At the termination ot' the transmission of the series of impulses, which results in the deenergization of relay 400, the entire mechanism at otliee X is again in its normal condition.

The release ot relay 400 results in the deenergization of relays 403 and 402, and upon closure of the normal contact of relay 400, a circuit is established extending from ground, through the normal contact ot relay 400, the right-hand alternate contact of relay 405, and the lamp 404 to grounded battery. The lamp 404 is lighted in this circuit to indicate to the operator` at Oi'lice Y that she may now withdraw the plug 407 from engagement with jack 408 of the toll switching trunk M.

At the time that relay 400 opens its outer left-hand contact, supervisory relay 410 releases. When this relay deenergizes relays 411 and 419 release and a circuit is established extending from ground, through the normal contact ot relay 410, the right-hand contact ot relay 411, the contact ot relay 419, the right-hand contact ot relay 413, winding of relay 416, and trom thence over the common conductor 417 to grounded battery, through the winding oi the relay in the transmitting mechanism TM, similar' to relay 200. The closure of this circuit operates relay 416 and the relay similar to relay 200 to initiate the operation of the transmitting and receiving mechanisms TM and RM. Tnasmuch as relay 414 is released at this time, it will be apparent that polarized relay 207 will not close its lower contact when the relay of the receiving mechanism RM, similar to relay 308, is operated, and therefore the conductor 223 will not be grounded to operate relay 112. Since relay 416 is operated, the positive. battery connected to the left-hand alternate Contact of this relay will cause the relay 207 to ground the conductor 224 latter the relay ot the receiving mechanism RM, similar to relay 310, is operated. The grounding of the conductor 224 at this time has no eliect since relay 112 lis not operated. During the operation ot the transmitting mechanism TM, the conductor 317 is grounded, as previously described, to short circuit relay 413 through the righthand contact ot relay 416, whereupon relai7 413 releases to cause the dcenergization ot relay 416 and the relay ot the transmitting mechanism TM corresponding to relay 200. Relays 411 to 416 and relay 419 are now in their normal condition.

Upon observing the lighted condition of the lamp 404, the operator at otlice Y withdraws the plug 407 from jack 408, thereby effecting the release ot relays 406 and 405 and the extinguishment ot the lamp 404, whereupon the apparatus of Fig. 4 is again in its normal condition.

At the time that relay 410 released following the deenergization of relay 400, relay 508 of the toll switching trunk M also rcleased. A circuit for supervisory lamp 506 is then established extending from grounded battery, through the lamp 506, the righthand alternate contact ot relay 502, the resistance 507, and normal contact or" relay 508. The lamp 506 is lighted in this circuit, and the operator atottice Z upon observing the lighted condition ot this lamp withdraws the plug 500 from the jack 501, thus causing the release ot' relay 502 to extinguish the lamp 506. Cut-ott relay 503 is also released when plug 500 is withdrawn from jack 501.

The toll switching trunk M and the substation line apparatus is now restored to normal.

Subscriber at substation S recalls the operator ab 077150@ X.

Should the subscriber at substation S beifore terminating the call desire to communicate with the operator at oi'iice X, this may be done by repeatedly opening and closing the switch hook contact at substation S. It will be remembered that while the receiver at the called substation isI ott the switch hook and the switch hook contact is closed, relays 410 to 416 and relay 419 are released. Upon the iirst opening ot the switch hook contact at the substation, supervisory relay 512 is released to cause the deenergization oit relay 509, whereupon relays 508 and 410 are brought into .series relation and relay 410 is energized. Then the alternate contact oi" relay 410 closes, relays 411, 412, 413 and 419 are energized over previously described circuits, relays 412 and 413 thereupon locking. T he energization ot relay 412 closes the previously described energizing circuit for relay 414 and the relay of the transmitting mechanism TM, similar to relay 200, whereupon a series ot impulses is transmitted by the mechanism TM over the path P to the receiving mechanism RM, the transmission of said series of impulses resulting in the grounding ot the conductor 223, and energization and locking oi relay 112 and operation and immediate release of relay 115, following which relays 113 and 114 operate. The ground at the contact of relay 114 is then extended through thc lett-hand normal contact ot relay 115 and through the resistance 111 to energize marginal relay 102 and light the lamp 117. During the transmission of the first series oit' impulses, ground is connected to the conductor 316 and extended through the right-hand contact ot relay 414 to release relay 412, following which the relay 414 is released in a manner which is now believed to be well understood. At the termination of the transmission of this series ot impulses, relays 410, 411, 413 and 419 are energized, relay 413 being locked.

The iirst closure ot the switch hoolr contacts at substation S following the first opening thereof again causes supervisory relay 512 to operate, whereupon supervisory relay 410 releases to open the circuits for relays 411. and 419. Although relay 411 is made slow to release, it is sufficiently tast in its operation to follow the opening and closing ot the switch hoolr contacts at substation S, but relay 419 is made very slow to release so that the same will maintain its contact closed during the short periods when the alternate contact of supervisory relay 410 is open while the subscriber is repeatedly opening and closing the switch hook contacts. Therefore, in response to the release of relay 410, relay 411 releases to close its contacts, but inasmuch as relay 419 does not close its contact, it will be apparent that the ground connected to the normal contact of relay 410 upon release thereof will have no effect since this ground is connected to the contact of relay 419 which is open. Then the switch hook contacts at substation S are again opened, relay 410 responds by closing its alternate contact to again close the holding circuit for relay 419 before the latter relay can fully release. The connection of ground to the alternate contact of relay 410 again establishes' the energizing circuits for relays 411 and 412, whereupon these relays again operate as before. The second operation of relay 412 initiates the transmission of a second series of impulses from oiiice Y to ofiice X which again results in the grounding of conductor 223 and the energization of relay 115. Relays 112, 113 and 114 being energized at this time, grounding of the conductor 223 has no effect upon the relay 112. Relay 115, upon being energized, locks through its left-hand winding and inner left-hand contact to ground at the contact of relay 114. Upon the closure of the outer alternate contact of relay 115, the interrupter 116 is connected in circuit with the resistance 111 to the' winding of marginal relay 102, and each time the brush of the interrupter 116 engages a nongrounded segment, the resistance 111 is removed from the circuit of the marginal relay and said relay thereupon releases to extinguish the lamp 117. Then a ground-ed segment of the interruptor 116 is engaged by the brush of the interrupt-er, it will be obvious that the lamp 11.7 will be lighted. Vhen relay 115 operates, it opensI at its right-hand normal contact the circuit of the slow release relay 113, which, after an interval, releases to cause the deenergization of the slow release relay 114. Then this relay releases, ground is' removed from its contact, and the locking circuit of relay 115 is opened and this relay thereupon restores to disconnect the interrupter 116 from the circuit of the marginal relay 102. The time interval between the energization of relay 115 and the release of relay 114 is sufficient to cause the lamp 117 to be iiashed seyeral times before the interrupter 116 is disconnected from the circuit of the relay 102, and while this is occurring, the switch hook contacts at substations S have again been opened and closed to cause the transmission of another series of impulses from oiiice Y to oiiice X, which again results in the gruonding of the conductor 223 and the reenergization of relay 115. Then this relay is released in response to the opening of the contact 114, the energizing circuit for relay 113 is again established through the right-hand contact of relay 115, and in response to the closure of the contact of relay 113, relay 114 is again energized. Therefore, when relay 115 is energized a second time in response to the grounding of the conductor 223, said relay 115 is again locked to ground at the contact of relay 114. The second energization of relay 115 again connects the interrupter 116 in circuit with relay 102, whereupon the lamp 117 is again iiashed. This operation continues as long as the subscriber at substation S opens and closes the switch hook contacts thereat, and the operator at oiiice X upon observing the flashing of the lamp 117 may communicate with the subscriber at substation S by 0perating the listening key 119 at the cord circuit A.

If after repeatedly opening and closing of the switch hook contacts* at substation S, the subscriber thereat should leave said contacts closed, that is, keep the receiver off the .switch hook, supervisory relay 512 will be energized, and the supervisory relay 410 permanently released. Following the deenergization of relay 410, relay 411 releases and thereafter relay 419 closes its contact since the alternate contact of relay 410 now remains opened. When the contact of relay 419 is closed, ground is extended through the normal contact of relay 410, the righthand contact of relay 411, the Contact of relay 419, the right-hand contact of relay 413, which wasl locked upon the first energization of relay 412, and from thence over the previously described circuit for relay 416 and the relay of the transmitting mechanism TM, similar to relay 200. With relay 416 operated, a series of impulses is now transmitted from office Y to oiiice X, similar to a previously transmitted series, which results in the grounding of the conductor 224. At this time, relays 112, 113 and 114 are operated, but relay 115 is released. Therefore, the ground on the conductor 224 is extended through the righthand contact and winding of relay 112 to cause the release of said relay, which is followed by the deenergization of relays 113 and 114. When the latter relay releases, ground is disconnected from the circuit of relay 102 including the resistance 111, and the lamp 117 is permanently extinguished. During the transmission of this last series of impulses to oiiice X to extinguish the lamp 117, conductor 317 is grounded and the ground connected thereto is extended to the winding of relay 413 through the righthand contact of relay 416, whereupon relay 413 releases. Following this, relay 416 deenergizes as previously described.

If after repeatedly opening and closing the switch hook contacts at subst-ation S, the subscriber thereat should replace his receiver on the switch hook to permanently ltllitltltltli.

open said contacts, relay 410 operates to maintain closed the holding circuit for relay 419 and to again cause the energization of relays 411, 412 and 413, whereupon another series of impulses is transmitted to oiiice X to ground the conductor 223, and during the transmission ot' this series of impulses, relays 412 and 414 are released as before described. The grounding of the conductor 223 again causes the energization ot relay 1.15 to connect the interrupter 116 in series with resistance 111, whereby lamp 117 continues to flash until relay 115 releases in response to the deenergization of relay 114. When relay 115 releases, relays 113 and 114 again operate, and the ground at the contact of relay 114 is now extended through the left-hand normal contact of relay 115, and from thence over the previously described circuits ot the resistance 111, to battery through the winding of the marginal relay 102. This circuit is now maintained closed so that the lamp 117 will burn continuously, .since no more series ot impulses are transmitted from otlice Y to oiiice X to again energize relay 115. The continued lighting of the lamp 117 now serves as a disconnect signal to the operator at oliice X, whereupon she proceeds to release the connection in the manner which has already been described.

Simultaneous or contemporaneous calls im'- tzaed at oy'oe Should the jacks of two or more transmission lines at otlice X be plugged into simultaneously, the common conductor 103 will be grounded by the individual mechanisms ot each line, and hence relay 200 will be operated to initiate the transmission o-ii a series of impulses from oiiice X to otlice Y in the same manner as previously described. When the group o't relays oct' the transmitting mechanism at oiiice X, individual to the line which is iirst in the order oi appearance, operates, the energization o1 the relay individual to said line, similar torelay 107, causes the transmission or the positive impulse over the common path l), which results in the energization of the relay individual to said line, similar to the relay 400, and the consequent lighting of the guard lamp individual to said line. ln the same manner a positive impulse is transmitted over the path P when the group of relays, of the transmitting mechanism individual to the next line in the order of appearance, operates. rlhus, during the one complete operation of the transmitting and receiving mechanisms it will be apparent that several positive impulses may be transmitted over the common signaling` path to eitect the operation ot a like number of guard lamps at oilice Y, individual to the various lines which have been taken for use.

If, after a call has been initiated at office X and the operation of the transmitting mechanism has been started, other lines should be taken for use contemporaneously with the operation ot said transmitting mechanism, it will be obvious that characteristic impulses Jior said other lines will be transmitted over the common signaling path provided that the relays of said other lines similar to relay 107 have been operated before the associated groups of relays of the transmitting mechanism individual to said other lines are energized.

Operation .of system with orom'ts arranged n accordance with Fig. l9.

llVith Figs. 6 and 7 introduced into the circuit in place el? Figs. 2 and 3, when the operator at olice X initiates a call by insert` ing plug 100 into jack 101, relay 103 operates as before and establishes the circuit for relay 107 which in this case now extends over the common conductor 103, and through the winding of relay 601 to grounded battery. Relays 107 and 601 operate, and the latter in closing its contact establishes an obvious operating circuit for relay 604. The closure of the contact of relay 604 con nects the ground at the contact ot rel( y 601 through the contact ot relay 604, and from thence to grounded battery, through the winding of relay 603, which is thereupon energized. Following the energization of relay 603, relay 602 operates over a circuit traceable from grounded battery, through the winding of relay 602, and the contacts of relays 603, 604 and 601 to ground. The closure of the Contact of relay 601 also establishes a circuit extending from ground, through the contact of relay 601, normal contacts of relays 629, 625, 621, 617, 613 and 609 in series, and the winding' of relay 632 to grounded battery. Relay 632 energizes and loclrs through its winding and contact to ground at the Contact of relay 631. When relay 602 operates, ground at the Contact of relay 601 is extended through the contacts of relays 604, 603 and 602, and from thence to grounded battery, through the right-hand normal contact and winding of relay 605. Relay 605 energizes and locks through its winding, and right-hand alternate contact to ground at the contact ot relay 631. The closure of the outer left-hand alternate contact of relay 605 establishes a circuit for relay 633 extending from grounded battery through the winding of relay 633, the outer left-hand normal contact of relay 607, the outer left-hand alternate contact of relay 605, and the contact of relay 601 to ground. Relay 633 energizes and locks through its right-hand contact to ground at the contact ot relay 631. The operation of relay 633 has no immediate eiiect. Upon energization of relay 605, a circuit is also established from 

